SF6 handling is the set of operations used to take gas out of a compartment without releasing it, filter and store it, pull a vacuum and refill. It is done with recovery and transfer units (Enervac GRU-7 and GTU) and auxiliary equipment such as the WIKA GPF-10 filter, the GVC-10 vacuum compressor and the GFU08 filling cart. IEC 62271-4 sets the procedure and IEC 60480 the criteria for reusing the gas.
What SF6 handling is
Working on a breaker or a GIS compartment often requires taking the gas out: to open a chamber, replace a seal, repair a leak or replace a component. The operation has four parts: recovering the gas without releasing it, cleaning it in the same unit, pulling a vacuum in the compartment and refilling it with gas of verified quality. Special units are used because SF6 is a greenhouse gas with a very high global warming potential, and because gas that has seen an arc contains decomposition products that are corrosive and toxic.
The reference standard is IEC 62271-4, which covers handling procedures for insulating and switching gases; IEC 60480 sets the criteria for reusing recovered SF6, and IEC 60376 the specification for new gas. This guide describes the equipment and what it does; the procedure for each compartment is that of the breaker or GIS manufacturer.
Enervac GRU-7 and GTU recovery units
Enervac manufactures SF6 handling units. The following can be drawn from the published information:
| Unit | What it does | Where it is used |
|---|---|---|
| GRU-7 | Recovers, filters and repressurizes; carries an oil-free high-compression-ratio compressor, a vacuum pump and several cylinders on a cart with pneumatic tires | Medium- and large-volume breakers and GIS compartments, in the yard |
| GTU | Recovers, consolidates and transfers gas, with filtration and drying; simpler and lower cost | Small-volume equipment and transfer between cylinders |
On the GRU-7 the gas goes through filters that retain particles and moisture when recovering and when repressurizing, and through a compressor that liquefies it or stores it at high pressure in the cart’s cylinders. Capacity, attainable vacuum and weight figures depend on the version and are set by the manufacturer in its datasheet. What matters when planning: the cart is the main piece of equipment in a recovery job on an HV breaker, and the transfer unit is the accessory that moves gas between cylinders.
WIKA GPF-10, GVC-10 and GFU08 equipment
WIKA publishes a family of SF6 service equipment with the following functions, according to its SP 63.xx datasheets:
- GPF-10, filtering unit (SP 63.11). Uses a replaceable “3 in 1” cartridge that retains particles, decomposition products and moisture, and protects the equipment downstream, such as the compressor. According to the sheet, filtered gas can often be reused.
- GVC-10, portable vacuum compressor (SP 63.13). Oil-free compressor that extracts the gas from the compartment; together with the GTU-10 transfer unit it reaches a residual pressure below 5 mbar absolute. Its inlet and outlet valves close by themselves, to keep gas from escaping to the atmosphere.
- GFU08, filling cart (SP 63.08). Modular cylinder transport cart in four versions; the E and C versions carry a vacuum pump to remove air from the compartment before filling.
- GVP-10, vacuum pump (SP 63.12). Rotary vane pump to evacuate air or nitrogen before filling, with a flow rate of up to 10 m³/h and an ultimate pressure of 0.02 mbar absolute or less.
The units complement one another: the filter cleans, the compressor extracts and the filling cart returns the gas to the compartment after a prior vacuum. A real job combines units from several manufacturers, and what matters is that each is suitable for the volume, pressure and gas of the equipment.
How the work is split in an intervention
- Before. A gas analysis is taken to know whether it is reusable: moisture, purity and decomposition products. See SF6 gas analysis.
- Recovery. The gas leaves the compartment into the unit and from there into the cylinders.
- Intervention. The mechanical work inside is done, with the precautions needed for decomposition residues.
- Vacuum. Air and moisture are evacuated down to the value defined by the manufacturer.
- Filling. The compartment is refilled with verified gas up to the rated density.
- After. Moisture and purity are measured, leaks at the connections that were touched are checked, and the mass of gas removed and replaced is recorded.
That list gives the order, not the procedure: pressures, times and sequences are those of the manufacturer and of IEC 62271-4.
What is weighed and what is recorded
The gas is accounted for. A useful handling record contains the mass of SF6 that leaves the equipment, the mass returned and the mass retained in the cylinders, with each cylinder weighed before and after. It serves to show that no gas was released and lets the owner keep the SF6 inventory of the installation. A cylinder of recovered gas is labeled as such so that it is not mixed with new gas.
Safety
SF6 is heavier than air and displaces oxygen in pits, galleries and GIS rooms. Ventilate and measure oxygen before entering. If the equipment has had arcing, the gas and the dust inside contain fluorides and sulfur in toxic, corrosive compounds: respiratory protection, gloves and waste handling are required. Cylinders work under pressure and are transported and stored according to the regulations for compressed gases.
How it fits with testing
Gas handling is almost never done alone. Before opening, the gas is measured; after filling, its quality is verified and the connections that were touched are checked for leaks; and when a breaker is worked on, timing, contact resistance and the mechanism are confirmed before returning it to service. For equipment that alarms on low density, see SF6 low-pressure alarm and density monitor.
Controlled, closed and sealed pressure systems are explained in controlled, closed and sealed pressure gas systems.
Do you need this test?
We carry it out for you: depending on your case we recommend the right test and equipment and include it in the quote, so you run the test your case really needs without paying for extra ones. Field work is in Colombia, or elsewhere on request.
See the scope of power circuit breaker testing and request your quote through the form.
Related guides
- SF6 gas analysis: moisture, purity and decomposition
- GIS substation
- Power circuit breaker
- Testing of primary substation equipment
- SF6 density monitor
- SF6 leak detector: WIKA GIR-10 and GA11 analyzer
- Gas systems: controlled, closed and sealed pressure
References
- IEC 62271-4, High-voltage switchgear and controlgear – Part 4: Handling procedures for gases for insulation and/or switching.
- IEC 60480, Specifications for the re-use of sulphur hexafluoride (SF6) and its mixtures in electrical equipment.
- IEC 60376, Specification of technical grade sulphur hexafluoride (SF6) and complementary gases to be used in its mixtures for use in electrical equipment.
- WIKA, datasheets SP 63.08 (GFU08), SP 63.11 (GPF-10), SP 63.12 (GVP-10) and SP 63.13 (GVC-10), SF6 gas solutions (wika.com).
- Enervac, product information for the GRU-7 and GTU units.
Frequently asked questions
Why can't SF6 simply be released when a breaker is opened?
Because SF6 is a greenhouse gas with a very high global warming potential, and because, if the equipment has had arcing, the gas contains toxic and corrosive decomposition products. That is why it is recovered into cylinders or into the unit, and the reuse criteria are defined by IEC 60480.
What is the difference between a recovery unit such as the GRU-7 and a transfer unit such as the GTU?
According to the manufacturer's information, the GRU-7 is a cart-mounted recovery unit with compressor, vacuum pump and filtration, intended for large-volume compartments. The GTU is a simpler transfer unit for recovering, consolidating and transferring gas in small equipment. The choice depends on the volume and on whether the compartment must be left under vacuum.
Does the gas have to be analyzed after filling a compartment?
Yes. A correct fill is verified by measuring moisture and purity, and by checking that there are no leaks at the connections that were touched. It is the natural close of any intervention and the reason gas handling and gas analysis are planned together.